2 files changed, 28 insertions, 0 deletions
diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
index 74c45d557a2b..2d3590cfb5e1 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
@@ -147,6 +147,7 @@ static void test_task_stack(void)
 		return;
 
 	do_dummy_read(skel->progs.dump_task_stack);
+	do_dummy_read(skel->progs.get_task_user_stacks);
 
 	bpf_iter_task_stack__destroy(skel);
 }
diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c b/tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c
index 50e59a2e142e..43c36f5f7649 100644
--- a/tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c
+++ b/tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c
@@ -35,3 +35,30 @@ int dump_task_stack(struct bpf_iter__task *ctx)
 
 	return 0;
 }
+
+SEC("iter/task")
+int get_task_user_stacks(struct bpf_iter__task *ctx)
+{
+	struct seq_file *seq = ctx->meta->seq;
+	struct task_struct *task = ctx->task;
+	uint64_t buf_sz = 0;
+	int64_t res;
+
+	if (task == (void *)0)
+		return 0;
+
+	res = bpf_get_task_stack(task, entries,
+			MAX_STACK_TRACE_DEPTH * SIZE_OF_ULONG, BPF_F_USER_STACK);
+	if (res <= 0)
+		return 0;
+
+	buf_sz += res;
+
+	/* If the verifier doesn't refine bpf_get_task_stack res, and instead
+	 * assumes res is entirely unknown, this program will fail to load as
+	 * the verifier will believe that max buf_sz value allows reading
+	 * past the end of entries in bpf_seq_write call
+	 */
+	bpf_seq_write(seq, &entries, buf_sz);
+	return 0;
+}